This invention relates to a negative photosensitive resin composition which is suited for use in the formation of pattern of insulation film, passivation film, .alpha.-ray shielding film, optical waveguide and the like, which are employed in various electronic parts. This invention relates also to a method of forming a pattern by making use of the aforementioned negative photosensitive resin composition, and to electronic parts provided with an insulation member or protective film member comprising a patterned polymer resin film.
In the ordinary semiconductor device comprising a semiconductor substrate, the surface of the semiconductor substrate bearing semiconductor elements is generally covered with a protective film called a passivation film for the purpose of improving the reliability of the semiconductor device by protecting the semiconductor elements from any influence by the outer environment. As a material for this passivation film, polyimide resin is extensively employed in view of its excellent properties such as electric properties, e.g. insulating characteristics, radiation resistance, environmental stability and heat resistance. Furthermore, this polyimide is widely employed in a semiconductor device as an .alpha.-ray shielding film, or as an interlayer insulating film for a multilayered wiring structure or for a multilayered element structure (a multichip module).
This polyimide can be easily formed into a film from polyamic acid which is a precursor for the polyimide. Namely, a varnish of polyamic acid is coated on the surface of a predetermined substrate and then the coated layer is heated to form a film of polyamic acid, which is then heat-treated at a high temperature thereby to cause a cyclodehydration reaction of the polyamic acid to take place, thus curing the polyamic acid film and forming a polyimide film. It is possible, with the employment of this method, to easily form a film of polyimide in spite of the fact that polyimide can be hardly worked since it is not or hardly soluble to most of organic solvents and is high in softening point. Therefore, the aforementioned method has been widely adopted in the formation of polyimide film.
Meanwhile, in the manufacture of a semiconductor device, various workings, for example, for forming a through-hole in a multilayered wiring structure or for forming a pad for effecting an electric connection with an external lead are required. In order to carry out these workings, a polyimide film formed as a protective film (passivation film) or an interlayer insulating film as explained above is required to be patterned thereby to form holes or grooves of predetermined patterns. Generally, the patterning of polyimide film is performed by making use of PEP (photo-engraving process) using a photoresist. Namely, after a polyimide film is formed on the surface of a semiconductor substrate bearing a semiconductor element thereon by the aforementioned method, a photoresist film is formed on the surface of the polyimide film and then subjected to a light exposure process followed by a development process thereby forming a resist pattern. Then, the underlying polyimide film is selectively etched by making use of this resist pattern as an etching mask thereby to form a polyimide protective film or interlayer insulating film having a prescribed pattern.
However, the aforementioned method of forming a polyimide pattern requires two independent steps, i.e. a step of forming a polyimide film and a step of the PEP, making the method troublesome to carry out.
With a view to solve the aforementioned drawback in carrying out the method, a method of patterning a polyimide film without employing the PEP has been demanded. In response to such a demand, a resin composition comprising a polyimide precursor has been proposed.
For example, Japanese Patent Unexamined Publication S/49-115541 discloses a polyamic ester which can be obtained through a reaction between a diamino compound and tetra-carboxylic diester dichloride. Namely, according to this prior art, instead of using tetra-carboxylic dianhydride which is commonly employed in the synthesis of polyamic acid or a polyimide precursor, tetra-carboxylic diester dichloride wherein a photopolymerizable group is introduced through an ester linkage is employed. This polyamic ester exhibits a photosensitivity of negative type so that an exposed portion irradiated with light is insolubilized against a developing solution. Therefore, it is possible to carry out a patterning in the course of forming a polyimide film without requiring the conventional step of PEP whereby to obtain a patterned polyimide film.
However, not only the process of synthesizing tetra-carboxylic diester dichloride having a photopolymerizable group, which is a raw material for the polyamic ester, but also the process of synthesizing the polyamic ester are very complicated. Moreover, the end resin product to be obtained contains unavoidably chlorine ions as an impurity. Additionally, since an organic solvent is employed as a developing solution in the process of developing a polyamic ester film, a large amount of organic solvent is required in the manufacturing line, which is undesirable in viewpoints of safety, sanitation and environment. Furthermore, the polyimide film pattern to be obtained may be accompanied with a swelling of pattern due to the development with an organic solvent, thereby deteriorating the resolution of pattern.
Further, Japanese Patent Publication S/59-52822 discloses, as a photosensitive resin composition of negative type as in the case of aforementioned prior art, a heat resistant photosensitive material containing a compound having a carbon-carbon double bond which is dimerizable or polymerizable by an actinic radiation and an amino group. However, this photosensitive material is defective in that, when it is employed as a passivation film for a resin-encapsulated semiconductor device, the adhesivity thereof to a semiconductor substrate, to a passivation film formed of an inorganic material for protecting the surface of substrate, or to a sealing resin is insufficient. Therefore, the employment of this photosensitive material may invite a problem that the reliability of semiconductor device thus obtained would be deteriorated. Additionally, this photosensitive material requires the employment of an organic solvent as a developing solution as in the case of the aforementioned polyamic ester, which is undesirable in viewpoint of safety.
On the other hand, Japanese Patent Unexamined Publication S/60-6365 discloses a photosensitive resin composition wherein the carboxylic group of polyamic acid is attached with a methacrylic acid (N,N-dialkylamine) alkyl ester as a salt. However, this photosensitive resin composition is defective in that the solubility thereof to a solvent to be used is poor.
Any of these photosensitive resin compositions are featured in that the light exposure portion of polyamic acid is crosslinked via the photo-polymerizable group thereof thereby turning it insoluble to a developing solution. This crosslinking however accompanies a volumetric shrinkage of the resultant film so that the film will be markedly thinned as a result of the light exposure and development process, and hence it has been difficult to form a polyimide film pattern with a high precision.
As mentioned above, a method of forming a polyimide film pattern without any employment of a photoresist has been recently tried with a view to simplifying the manufacturing process, and as a result, a photosensitive composition exhibiting a photosensitivity through the attachment of a photopolymerizable group in the form of ester or salt to the carboxylic group of polyamic acid has been developed. However, these conventional photosensitive compositions are accompanied with problems that, due to a structural restriction of polyamic acid, the synthesis thereof is difficult or the adhesivity thereof to a substrate for example is more likely deteriorated, and that, since the polyimide film to be obtained will be markedly thinned as a result of the light exposure and development process, it is difficult to form a polyimide film pattern with a high precision.